The growth in the use of transceiving devices, such as portable cellular telephones, is a testament to the devices' convenience, availability and value. The quality and the availability of cellular telecommunication services have dramatically influenced the public's acceptance of this technology. The growth of the cellular industry has been significantly accelerated due to many improvements in the transmitting and receiving of signals.
In earlier days of cellular technology, a typical cellular transceiver comprised a handset hardwired to a base unit. An example of such a transceiver is a unit that included a handset and a base, all of which was to be carried in a tote bag. The handset included a dialing keypad and circuitry for providing convenience features such as automatic dialing memory. The base housed the transceiver circuitry and a battery. An external antenna, oftentimes fixed, was connected to the base unit.
In time, the technology evolved until, today, cellular transceivers are known that are pocket-sized and hand-held. These modern cellular transceivers provide the traditional equipment described above, but the transceiver circuitry, battery and antenna are contained in a single unit or case.
Various types of antennas are known for use with modern cellular transceivers. One such is a fixed rod antenna. Rod antennas have traditionally been affixed rigidly to the transceiver case and, consequently, extend from the case at all times. This type of antenna provides good transmission and reception, but is not convenient for users. Such transceivers are difficult if not impossible to carry in a shirt or coat pocket. The user oftentimes finds the device to be unwieldy due to the protruding rod antenna.
Alternatively, retractable rod antennas have been used and are known in the art. A retractable rod antenna is preferred for convenience reasons, as the antenna may be readily withdrawn and substantially contained within the transceiver case. This is much more convenient for the user. When a retractable rod antenna is provided, some portion of the antenna must yet be active, even when the antenna is fully retracted, so as to allow the transceiver to receive a call signal while in the "stand-by" or "receive only" mode of operation. Compound antennas have been proposed to address this concern. Compound antennas provide a primary antenna element that can be retracted into the transceiver case and a secondary antenna element that remains outside the transceiver case to facilitate operation in the stand-by mode. The secondary antenna element is conventionally attached to the primary antenna element. The secondary antenna element remains active for receipt of an incoming call signal. An example of such a retractable, compound antenna is shown in U.S. Pat. No. 5,204,687, issued to Elliott et al.
Further, it is desirable to be able to conduct some communication, even if only over a limited range, without having to extend the antenna. Therefore, it is preferred that the secondary antenna element should also be useful for transmitting. However, the retracted primary antenna element will also radiate when the transceiver is transmitting. This radiation may be coupled back into the transceiver circuitry and interfere with proper operation thereof. To reduce this problem, some antenna assemblies have employed switching arrangements that, upon retraction of the primary antenna element into the transceiver case, de-couple the retracted primary antenna element from the transceiver circuitry and then couple the secondary antenna element to the transceiver circuitry. This type of switching arrangement is shown in the Elliott et al. patent.
Alternatively, other assemblies shield the antenna within the transceiver case to prevent radiation emitted by the retracted primary antenna element from causing interference with the transceiver circuitry.
Another alternative antenna assembly includes a retracted antenna and a separate internal antenna, for stand-by operation, enclosed within the cellular transceiver case. Such an antenna arrangement is shown in U.S. Pat. No. 4,862,182 to Egashira. This alternative antenna assembly requires expensive and relatively bulky switching devices to de-couple the retracted primary antenna and couple the internal antenna. The extra space required for the separate internal antenna and the weight of the internal antenna increases the overall size and weight of cellular transceivers employing this type of antenna assembly.
Thus, many prior art antenna arrangements have placed significant restrictions on the design, cost and use of hand-held cellular transceivers. Shielding and switching devices necessary to allow extendible antennas, complemented by either a compound antenna or an internal antenna, have added cost and weight to these hand-held cellular transceivers. Such additions have made the use and operation of these transceivers less convenient. Further efforts to reduce the cost, weight and size have been stalled because of the limitations of these current antenna designs.
What is needed and what is not available is a retractable antenna for use with a hand-held cellular transceiver that is small, light in weight and relatively inexpensive. The needed retractable antenna must provide satisfactory operation in both the retracted and extended positions so that satisfactory transmission and reception may be achieved and not degrade the performance of the radio by internal electromagnetic radiation emitted from the retracted portion of the antenna.